1. Field of the Invention
This invention relates to devices and equipment for suspending tubing in an oil or gas well and more particularly, to a new and improved tubing anchor assembly for suspending coiled or conventional tubing in a well without the necessity of "killing" the well. The tubing anchor assembly of this invention is characterized by multiple, shaped slip segments located in the slip bowl of a conventional tubing head, each of the slip segments provided with a vertically oriented dove tail slot which cooperates with the frustro conical tip of a slip retainer screw threaded in the tubing head and projecting into the slip bowl, to facilitate release of the slip segments after a length of tubing has been inserted into the well, in order to support the tubing in the well.
As the down-hole pressure in oil and gas wells decreases with time, it is sometimes desirable or necessary to insert tubing in the well in order to provide a means for more readily removing fluids from the well and prolonging the life of the well. Traditionally, it has been necessary to "kill", or terminate production by application of hydrostatic pressure in the well in order to achieve this objective. The well is "killed", or production is terminated from the well by pumping a fluid such as water into the producing interval to create a hydrostatic head in the well of sufficient magnitude to overcome the well pressure, thereby terminating production. One of the problems inherent in "killing" a producing well which is characterized by relatively low pressure, is the difficulty and sometimes impossibility, of restoring the well to production after the desired swabbing or cleaning operation has been accomplished. Such cleaning and swabbing and other well maintenance operations are expensive, generally because of the time required to remove the Christmas tree, set up the necessary apparatus for maintaining the well, placing tubing in the well, where such tubing is deemed necessary, placing a tubing head on the master valve, setting the slip segments and the necessary packing, replacing the Christmas tree and then attempting to bring the well back into production. It is apparent that if the well cannot be brought back into production, then the time and money expended for placing the tubing in the well, as well as the maintenance effort, has been wasted.
2. Description of the Prior Art
Slip assemblies and related equipment have been employed for many years in the oil field for suspending pipe and tubing in oil and gas wells. Such assemblies usually consist of multiple, segmented wedges which are tapered and are provided with horizontally extending teeth located on curved inner surfaces, which teeth are designed to engage and cut into the pipe or tubing to prevent relative movement between the tubing and the slips. The slips are wedged-shaped and curved in order to conform to the shape of a tapered, usually conical slip bowl provided in a tubing head, in order to facilitate engagement of the slips radially about the pipe or tubing when the slips are released inside the slip bowl responsive to contact between the wedge-shaped rear surfaces of the slips and the slip bowl in the tubing head. Lowering of the pipe or tubing after release of the slips results in a radial compressive force which urges the segments against the pipe or tubing until the teeth cut into the pipe or tubing wall sufficiently to support the weight of the tubing in the tubing head. Generally speaking, the teeth provided in the curved inner face of each slip segment are configured and oriented to engage and cut into the pipe or tubing in an optimum manner, to prevent relative movement between the slip segments and the suspended pipe or tubing.
Various devices have been known in the prior art for supporting casing and tubing in oil and gas wells. An early "Pipe Holding Device" is disclosed in U.S. Pat. No. 1,836,596 dated Dec. 15, 1931, to J. E. Hoffoss, et al. The "Pipe Holding Device" of this patent includes a single slip which is adapted to entirely surround the pipe and the device includes multiple jaws so mounted and constructed that they can be handled by one workman to engage the pipe uniformly and evenly on all sides. U.S. Pat. No. 3,051,513 to J. D. Watts, et al, dated Aug. 28, 1962, discloses a "Hanger Assembly and Seal Therefor", which includes a wrap-around hanger assembly having upper and lower segmental members cooperating to define a tubing support bowl and a casing head engaging ring, respectively. The segmental members forming the bowl and ring are interconnected in pairs by an improved construction which provides limited vertical movement between the ring and bowl and allows relative rotational movement between these two elements. A "Slip Assembly" is disclosed in U.S. Pat. No. 2,874,436 dated Feb. 24, 1959, to H. Allen. The "Slip Assembly" of this invention is characterized by a slip bowl constructed in two sections, each of which is substantially semicircular in configuration, in order to permit separation for ease of placing the assembly in position around a pipe to be suspended. Semicircular portions of the bowl are secured around the pipe by cap screws and define a bowl which is in effect, a complete circular structure having an outer tapered surface and an inner tapered surface which are substantially parallel to each other. A plate which serves as a slip retainer is also provided on lateral edges of the slip bowl segment. A "Casing Hanger and Stabilizer" is disclosed in U.S. Pat. No. 4,334,342 dated June 15, 1982, to Gregory G. Hall, which device includes a pair of generally wedge-shaped slip segments having mating faces and removably joined at the faces by a pair of plates. The device is further provided with interior slip threads or teeth for engaging the surface casing and a plurality of slots in the longitudinal exterior surface to permit the pumping of drilling mud or other fluid between the supporting conductor pipe and the suspended surface casing prior to cementing the surface casing in the conductor pipe.
U.S. Pat. No. 2,887,754 dated May 26, 1959, to C. F. Johnson details a "Pipe Anchor" for suspending pipe in a well which includes a support with a central opening for the pipe, wedges disposed in a conical bowl in the support and screws inserted in the support wall and engaging the wedges, which screws are sheared when the wedges are forced downwardly against a length of pipe inserted for suspension in the support.
It is an object of this invention to provide a new and improved tubing anchor assembly for suspending tubing in a well in a safe, fast, efficient and cost effective manner without the necessity of reducing production pressure in the well prior to insertion of the tubing.
Another object of this invention is to provide a tubing anchor assembly for suspending tubing in an oil or gas well, which assembly is characterized by multiple slip segments, each having a dove tail slot provided therein for engagement with the shaped end of one of several slip retainer screws which are threaded radially in a tubing head to facilitate controlled release of the slip segments in the slip bowl of the tubing head to support tubing placed in the well while production pressure is maintained in the well.
Yet another object of this invention is to provide a new and improved tubing anchor assembly for use in tubing heads to suspend tubing in oil and gas wells without "killing" the wells, which assembly includes as a first element, multiple slip segments clustered in a slip assembly by a retainer ring and disposed in the slip bowl of the tubing head, each of which slip segments is provided with a dove tail slot in the rear surface thereof and as a second element, slip retainer screws radially threaded in the tubing head wall and extending into the slip bowl and engaging the slots in the slip segments, to selectively release the slip segments in concert and support the tubing after the tubing is run into the well.
Yet another object of this invention is to provide a tubing anchor assembly for use in conventional tubing heads, which assembly includes at least two slip segments loosely joined by a ring and having vertically oriented dove tail slots provided in the outside surfaces thereof and positioned in the slip bowl of the tubing head and a slip retainer screw for each slip segment, which slip retainer screws are threadably and radially pressure sealed in the tubing head and are each provided with a frustro conical tip which extends into the slip bowl and engages a dove tail slot in the slip segments to selectively retain the slip segments in the slip bowl of the tubing head and threadably extend the slip segments into the slip bowl and allow the slip segments to release from the frustro conical tips of the slip retainer screws by operation of gravity, to engage and support the tubing in the tubing head while pressure is maintained in the well.